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When you’ve just had a baby, the emphasis on breastfeeding is so strong that you may struggle to source any non-biased information about formula feeding.

Nearly 8 in 10 of us who formula feed have never been told or shown how to prepare a bottle by a health professional, according to a Food and Drug Administration study in the U.S.

This figure is alarmingly high and shows how much moms have to rely on each other—and “Dr. Google” to find information. 

But the facts out there can be unclear or difficult to find (especially when sleep-deprived).

One topic that is consistently debated is about water: is tap water or bottled water best?

You won’t be surprised to learn that there’s not one clear answer, with much confusing and conflicting advice on offer.

So June has done the research and spoken to experts on your behalf to get to the bottom of this overly complicated topic. 

Q: When I make up my formula, should I worry about using tap vs. bottled water?

A:  The easy answer is: No. The more complicated answer: It depends where you live.

In the majority of developed countries, both are safe to use however it does depends on the quality of the water that comes from your tap.

The quality of your tap water depends on where you live

Q: What am I looking for in terms of water quality?

A: You’re looking for a water that has no contaminants and has relatively low mineral levels. 

“The main difference between tap water and bottled water is on one hand the sterility of the water, and on the other its chemical makeup,” says Dr. Robert Cohen, Vice President of the French Society of Pediatrics.

“When minerals are too prevalent in water, this could cause mineral levels in the body to become too high (such as salt and potassium), which puts too much strain on a child’s kidneys,” he adds.

Q: How could this affect my baby?

A: If your tap water is full of nitrates for example (a compound that occurs naturally in certain foods as well as in soil fertilizers) these could be transformed into negative nitrites by your child’s intestinal flora.

“These nitrites could cause the potentially serious illness called methemoglobinemia (often called ‘blue child syndrome’)”, Dr. Cohen explains, which affects the ability of hemoglobin to carry blood around the body.

Q: How do I know what’s in my tap water?

A: It’s impossible to know just by looking. Technically the government should regularly monitor the safety of tap water, but good luck getting this information!

In countries like Hong Kong, old pipes can lead to the introduction of materials like lead into the tap water. 

But you can buy reliable at-home test kits which will test for a number of contaminants such as lead, pesticides, nitrates/nitrites and chlorine. 

TIP: Intertek is one company that can test for lead, cadmium, chromium and nickel in your tap water from HK$280.

 Q: How do I make my tap water safe for me and my baby?

A: To be sure your tap water is safe to drink, you might think about installing a water filtration system. 

If you install one directly on the tap there is a potential for bacteria to breed around the filter, so it’s recommended that you follow the manufacturer’s advice and ensure the cartridges are changed regularly. 

Other options include filter jugs or containers that fit into your fridge.

A water droplet

Your best options are tap water or low-mineral bottled water

Q: So is bottled water the better option?

A: Opinion is divided as to whether it’s safe to use bottled water and it comes down to the mineral content.

The U.K’s National Health Service says if bottled water is used, the sodium content should be less than 200mg/l and the sulfate levels no higher than 250mg/l. 

In France the sulfate recommendation is lowered 140mg/l (to mirror the levels its scientists found in breastmilk).

In the U.S. and France, bottled water is more commonly used but water brands will display a label certifying it is safe for bottle preparation.

In Hong Kong there are no regulations and many brands will not even reveal the mineral content of their water. In this case, it’s best to opt for an international brand that clearly tells you the sodium and sulfate levels.

We have compiled a table of the advised mineral make-up of water that is suitable for use for babies:   

Table showing the mineral make-up of water

Q: Is it safest to avoid bottled water that has minerals then?

A: Your best options are tap water or low-mineral bottled water.

 “It’s impossible to make a water without any minerals at all,” says Dr. Cohen. “In mineral waters that say they’re suitable for the preparation of baby bottles, the mineral levels are limited but they’re never totally demineralised.”

Q: Are there any benefits to using mineral water for children?

A: With bottled mineral water, you know exactly what the mineral make-up is from the label—so it’s possible to choose one that’s well suited for formula prep. 

Especially if you live in a country like Hong Kong where the tap water may be unreliable, bottles provide some knowledge and comfort. 

However, it’s not necessary to choose a mineral water for the nutrient value it provides to your baby, as these needs are already met by the formula itself.

TIP: If your baby is constipated, a highly mineralized water can help induce bowel movements. Dr. Cohen recommends one bottle a day for several days made with high levels of sodium, calcium and magnesium to trigger osmosis in the digestive system.  

Q: What’s the final advice?

A: Whichever water you use for formula feeding, it’s advised to boil it first to get rid of any bacteria. After the age of one, your child’s immune system is more developed and there’s no need.

Boiled tap or bottled water should then be left to cool to no less than 70°C, but in reality, few moms ever measure the bottle temperature.

The generally observed rule is to cool formula until it’s acceptable to drink and leave it out for no longer than 30 minutes (always check the formula instructions first).

Q: What about when I’m outside the home?

A: If you’re just popping out for a short trip, filling up a vacuum flask with boiled water before you leave the house is a reliable option. 

Pour the water in hotter than you’d usually use it and it has the potential to last you all day.

If you’re without your flask, the safest option is to buy a low-mineral bottled water and ask someone to boil it for you. 

Dr. Robert Cohen is a pediatrician at Creteil Hospital in Paris, France. He’s also Vice President of the French Society of Pediatrics, President of the Pediatric Infectious Diseases Society and Coordinator of InfoVac France.